Project summary Stem cells give rise to all tissues during development and are essential for maintaining tissue homeostasis in adults. To divide, stem cells must replicate their contents, imposing a large requirement for nucleotides, amino acids, and lipids. Therefore, most stem cells are programmed to respond to nutrient availability and dynamically adapt their rates of proliferation in response to nutrient flux. Emerging evidence indicates that stem cells typically rely on metabolic programs distinct from those used in other cell types in the same tissue. Misregulation of metabolic processes can uncouple cell proliferation from nutrient availability, and cancer cells frequently hijack cell growth programs to escape nutrient dependence. Therefore, precisely how stem cells restrain their proliferation in response to nutrient availability is a fundamental open question in stem cell biology with important implications for understanding the molecular basis of cancer. This project seeks to elucidate the cell-intrinsic mechanisms that couple stem cell proliferation with nutrient availability. Neural stem cells in the Drosophila central brain, termed neuroblasts, provide a unique system to study links between nutrition and stem cell proliferation as there two distinct subtypes that respond differently to nutrient availability despite sharing an extracellular environment. Moreover, systemic nutrient signaling to neuroblasts can be experimentally manipulated by varying larval diet. My preliminary data from this model indicates that a genetic program controlled by the Eyeless (Ey) transcription factor, homolog of mammalian Pax6, is both necessary and sufficient to drive nutrient-insensitive neuroblast proliferation. Other recent work has demonstrated that another transcription factor, Prospero (Pros), initiates developmental quiescence in some neuroblasts, but its role during nutrient restriction and its relationship to Ey are completely unknown. The first specific aim of this proposal will test the functional requirement for Pros in nutrient-induced neuroblast quiescence and determine if Pros activity is repressed by Ey in nutrient-insensitive neuroblasts. My preliminary data also suggest that nutrient-insensitive neuroblasts are metabolically distinct from those sensitive to nutrient restriction, both in the way nutrients are metabolized and how cellular growth signaling is maintained. The second aim seeks to better understand these differences and their contribution to nutrient-insensitive neuroblast proliferation by testing key biosynthetic pathways and cell-autonomous TOR cellular growth signaling for a functional role in nutrient-insensitive neuroblast proliferation. The results obtained from this project will lead to a better understanding of the ways in which nutritional demands are addressed in stem cells and indicate possible approaches to enhance stem cell therapies by modulating stem cell metabolism.